1. Field of the Invention
The present invention relates generally to optical discs, apparatuses and methods for recording and reproducing data and, more particularly, to an optical disc in which a pregroove is wobbled to record address information so that data can be recorded or reproduced at correct positions, and a recording apparatus and a method which enable data to be recorded or reproduced at correct positions on the optical disc.
2. Description of the Related Art
When data is recorded on a disc, there is a need to record address information so as to enable the data to be recorded at predetermined positions. In some case, such address information is recorded by wobbling.
That is, as shown in FIG. 20, a track on which data is recorded is previously formed as a pregroove, and side walls of this pregroove is caused to wobble (meander) in accordance with address information. Addresses can be read from wobbling information recorded in this manner, thereby enabling data to be recorded at desired positions.
The method of recording addresses by wobbling as described above entails a problem described below. In a state where no data is recorded in the pregroove (track), addresses can be accurately read out to enable data to be recorded at correct positions. However, if data is recorded by forming, in the track (pregroove), regions (pits) differing in reflectivity from other regions (regions in which no pits are formed) (for example, in accordance with the recording method for discs capable of rerecording), changes in reflectivity due to wobbling and changes in reflectivity due to recording data (pits) interfere with each other to make it difficult to correctly reproduce addresses (wobbling information). As a result, it is difficult to record data at correct positions.
Then, a method may be taken into consideration in which address information is included in the data to be recorded on the track, and in which recording positions are determined on the basis of the address information.
However, in the case of recording, for example, data for computers, the data is not continuously recorded in serial order from the starting end to the terminal end of the track (pregroove) but intermittently recorded at predetermined positions, as shown in FIG. 21.
That is, the track is divided into a plurality of cluster regions (or sectors) to record a cluster of data in each of the cluster regions. Each of clusters of data recording in this manner do not follow immediately after the preceding cluster of data.
If data is recorded intermittently in this manner, addresses are also recording intermittently with respect to clusters. However, some amount of error occurs in determining the recording position of each cluster of data. Therefore, if recording is performed on the basis of addresses previously recorded, errors of the recording position may accumulate to such an amount that interference occurs between adjacent clusters (sectors), as shown in FIG. 22. That is, the recording region for a terminal end portion of one cluster overlaps a start portion of the next cluster.
To prevent such interference, a buffer region in which essentially no data is recorded may be formed between each adjacent pair of clusters, as shown in FIG. 22, for example. However, the effective recording capacity of the disc is reduced if such a buffer region is formed.
Thus, with respect to the disc in which data is recorded randomly (intermittently) as shown in FIG. 21, it is difficult to record addresses by wobbling and to correctly record data at predetermined positions on the basis of the addresses.
The density of wobbling information is much lower than that of recorded or reproduced information. Based on such wobbling information, therefore, the recording position of each sector cannot be determined finely and an error can occur in determining the recording position of each sector. Also for this reason, the possibility of interference between adjacent sectors is not negligible. Also, there is a need to absorb jitter due to an eccentricity or the like. To avoid such undesirable conditions, a substantially large amount of non-recording buffer area is required. Use of a large recording buffer area is disadvantageous considering the data capacity. A considerably redundant system results thereby, such that it is difficult to perform high-density random recording and reproduction.
Further, random data recording and reproduction on a programmable optical disc necessitates formation of a variable frequency oscillator (VFO) region or the like in which data for pulling into a phase lock loop (PLL) circuit for generating a clock as a basis for recording and reproduction is recorded as well as addresses such as track addresses and sector addresses. In the case of a system for recording data including addresses and so on, it is necessary to set, in front of each recording sector, a linking sector in which dummy data for changing a preceding reproducing state to a recording state is recorded.
As described above, in order to actually record data randomly on an optical disc, it is necessary to form regions in which addresses for the data and VFO data are recorded as well as essential regions for recording data. The methods heretofore proposed, however, increase the overhead, so that the effective recording capacity of the optical disc is reduced.
In the conventional compact disc read only memories (CD-ROM) and the like, a sync signal "frame sync" is recorded in a certain cycle. Sync system processing is performed on this unit sync signal. However, if a read only memory (ROM) disc and a random access memory (RAM) disc are formed so as to have the same format with the addition of a header, the header disables the sync system from being continued with respect to unit recording sectors and makes the sync system processing difficult.